FR5S KITCHENsimsongP~:+ 8?;+S &ۆ CG6  , +Y/(i9l}-"  xEnglish EnglishTimes New Roman" STATE OF THE ART, -->>`m44Tc{{55Yi->`m4Tc{5Yi׸1Xu(English EnglishTimes New Romanlby P.J. Plauger-'I$IVV~v|//Q"Oef}f}}$}$ -'I$V~v|//Q"Oef}ƨya NZHL{zDEnglish EnglishTimes New RomanArial*Reprinted with permission from EMBEDDED SYSTEMS( PROGRAMMING, March 1994. (C) 1994 MILLER FREEMAN, INC( via Copyright Clearance Center, Inc.0"MhUhToUhOhUhPhVi OiO$j$V;i=PBiCQMjMO^i^OkjkW{q}ViViWjPiWjWjPjWjW j PjP"j#W-i-W>jAWZjZPgjgP{j}PjPkPjPkQjPkP'k'P3k3PHkIP`k`PvkvQkPjQkPkPkxyxyyzz58zQUzZ]ztwz{{{{  |{01|CD|VX]]{ss{|}{{{||||{{{"&{89{KM{ac{yy{{{|{|||).22|AA|FJ|^`{w`{w 13GJ^auu,,7<PTgltltMqj0xw6t$MwzMhUhToUhOhUhPhVi Oi$V;i=PBiCQMjMO^ikW{q}ViViWjPiWjWjPjWjW jP"j#W-i-W>jAWZjgP{j}PjPkPjPkQjPkP'k3PHkIP`k`PvkvQkPjQkPkxyxyyzz58zQUzZ]ztwz{{ |{01|CD|VX]s{|}{{||||{{"&{89{KM{ac{y{{|{|||).2A|FJ|^`{w #&9>KPX\qv 13GJ^au,7<PTgltb-G%rLEnglish EnglishTimes New Roman'l Chocolate  H H/F+nFmHH FLHCoFiFiF   HF H H/F+nFmHH FLHCoFiF&ƕ+*^i"1English EnglishTimes New RomanArial|M\T      9N;9ی^ ,h, English EnglishTimes New RomanU.any years ago, a friend told( me about an interesting em( bedded application. It seems( the owner of a small bakery decided to( automate the tedious business of baking( the various breads and pastries every( night. These were the days of minicom( puters (remember those?) and labor( shortages (remember those?), so it ac( tually made a kind of sense to replace( the midnight shift with a dedicated ma( chine and a mess of Fortran code. '(&'#NJ*+==PP^^rq  --:9FGPRabsu58GGSSefxy!#/1@AMNZ\dfwy* , ; <N Ob d t t    ( '       ) + < >D DT T^ `l lw w           4M2N;N;N;N:M:N;N;N;N</O02>N>2GNG;WNW;cNc;pNq;O<N2N1N1N2O;N2N< N ;N:*V*24N42FNH;XNX;gNi2qNr1N;M2N2N6M:N:N~h|i|d{h|j}i}e}j|d}d!|!a4}5jD}DeK}KeV|Wkh}g`{}|`}j}j}j}a}a}j}i}a}j}j"|#i/}1j<}<jD}DjU}V`d}d`h}haz}|j|`}a}i|ii~  **::MN\]mn~   ,-99Q9QRbbnn~  )*::AA[Zkkyy**99>>\\ggyz}       : ;L Kj k} ~          5 5F GY [m m       }#77#7$7 7$7$?%7$77'='%585%F7F$d8e%v7u$88%7%8 7 77%8$7$!7#184?=C2J=J$W8W$c8d$u7u7777$7#7,0,0~MeReReIfJfRmRgSgSfJ$f&S6f6SCfCSSfSKbfbKtftJfSgIfIfRfJfJfSfSfS fReR+e+N8f8NCeDRUeURbfbSnfpSeRmJfSeReSfSf~|wwxw  !y25|??|GGTVxhjxstx||x|yyxx  x-0x8:IK[]}hixyww}((22NP`amo{{  ((78JJ\^motot ( 1VN'~`}(~&~'} #}?7'~Imf'~w(}t!}W..As you might expect, the fellow( charged with writing the code knew( next to nothing about baking. Even( more naturally, the owner of the bakery( took it for granted that he could explain( all the mundane details of the business( well enough for the programmer to do( his job. No need for any fancy systems( analysis or design reviews. That stuff( was for large insurance companies and( government contracts. ##R(%'c  88UW_ars  ,,78JL\\ss|    &    #$--::MMaa y{{  '  '' 57 GG[\ kk~~    |9M9L8L5L4M4L:M9M9L:*M*56M61IMI0TMT:fMh:{T{:N:N1M:M:M5L1M1M: L!14M31=M>:PMR:cUeHkMk1M1M9K9L:M:M|g{g{g{h{g{gzh{b{hzh%|&h7{8_A{B_L{Kh^\vbbcl{lcx{w_{h|h{h{h{h{h{h{h{h{_){)_-{-c9{:_M{Nh^|^_e{e_w{xhz`{h{hzgg|)(67HI\\iizz(':;EEYY``po},->ARTdgww"#57FFQQbdvw|  !33@@NM]^llxx78VWfgtt|44 34< 44/444!%5%!/4/!@4B!R5S"b4cu4u45!5!4!4!4!5!<44!4!)5, ;4<!N<N!X4X!c4e!v<x 44!4 4 4 4|OcObOcFcOjObFcOcOcOcP#c#F3b3FEbGPWcXPdcfFocpOjOcObObPcObFcObOb Ob]bG/b/GFbHFYc\PlbnJybyJbObKbObFbEbEbz}}}tt}~uu~ ~02~AAuLLuVW~hj~vw~~~~~~~~  ~(*~;=~NP~abulm~|}}}~}tt{%%1199JJ[\on{{  |'#|0UM#|_{(|*}(|%|<4'|Ejb'zt&{zX..So the programmer set to work and( eventually started having some suc( cesses. Many a morning, the owner( would find that his mini automated( bakery had turned out the stuff he had( asked it to do the night before. The stuff( mostly even tasted okay. But not always.( It seems that the spoilage rate had gone( up considerably since he dismissed the( midnight shift and started depending( on the computer. "FJ+))'%  ()66II[Zij{|  ""44==XWiivwz #--:;GF YY ghuu  #++89JJhiyy{6I6I6I6J7I6IDI-J-J7)J*6<J<6PQP6eJe7vJv7J7J7J7J6J-J7J6 QDO1,J,16I7-IIK7[J[6pJp6I6I6I6I6J6Jzdwdxdx[x[x[x\x\xey\%y%\;x;`HxH]Zy[elxo`yxy\x\y[xeyeyey\xe x [x[*x*e:x<dNwO`[x\dlxndxex_wdw[w[w{&&22==PR_`ru  #%00CDRR]]ffxzz,->>FFQRefvv}}#%36;;DD\]prz ((//:;LNZ[ghxx %%57HITT[[kmwv y211221221 1 2.20=1=D1DQ2Pc2dt1t|1|2:2221922 2 2 +1,:1:C1CV2Wi1i{1{191111yL`LhL`L`L`MaM`C`C _ N`M*`+M<`<DPaPDZaYMlhlMwawNaD`M`L`M`C`C`M`C`C_CaM(`)LG`GDQ`RL^`_Ll`mL~_~C_C`G_C`L_L_y{qr{q{rvv|"#r56rA@sOMwZZwjj{{||rr|w||v|  rq--q>@{PQ{cd{tt{rq{{{x11FERRbbppvpv "z#${-QJ"z[yx#{'z+z )y:1)yCh`'yq%xvxU/.Some of the early botches were( scenes straight out of Robot Theater. A( water valve would stick open or an in( gredient would run out and the system( would doggedly persist in trying to( knead, shape, and bake worthless goop.( The hardware types kept adding sen( sors and the programmer kept adding( checks, until the worst gaffes were( brought under control. As a final cop-( out, the computer got its own autodialer( so it could wake up the owner in the( middle of the night and have him come( straighten out messes. O&$'$$$'$%='(55MMXXkm||  )*9;MO^_kky                      % & 7" 8K M X X a a r r                  & &= >Q S b c t u           x4 F 4 H / G 4 G 4 G 4 G 4 G 4 H + H 5 H 5 *H *4 5H 55 NH O5 `H `4 sH t, ~H ~+ H + H 4 H 0 G + H 4 G + H + G 4 G 4 N 5 %G &4 7G 74 EG E4 VG W3 cG c3 qG q3 G 3 G * G * G 4 G ; ? ; ? yc ~ c v d w Z v Y v c w c w ^ v ^ v c v c ,w -c @w A[ Jw LZ ^w ^Z jw jc vw wc w c v c v c w c v ] u ] v c v b v Y v Y (v (] 3u 4Y Fv Gb Xu Xb bv bb nu pb } b u ] u b u b u b u x                 # $ 4 6 F H Y Z d d v v                     ! ! : : E E S T e f p o            x                     - . ? ? F F P P a b u u                     ' ' 9 : D D U U b b p p y y            x                 & & 7 9 G G W W f f r q                     % & 9 9 L N X X j l ~ ~            x 0  0  1  1  1  1  1  0  0  1  &1 & 61 6 D1 D V9 V d1 d v1 v 8  0  0  0  0  0  /  0  $0 $ 4/ 3 F6 F S/ S `0 ` q. r /  .  /  /  7  7 yK _ B _ L _ K ^ B _ L _ Z e K ` K ` L &_ 'F 2_ 4B >` >C H` HC `_ `G l_ lC ~_ L _ K ^ K ^ K ^ K ^ K ^ E ^ E ^ J $f %J 5] 6@ D^ >A O^ NJ ]] ^I j] jI ^ I \ J ] J ^ J ] J ] xq  z  z  y  z  q  u  u  z  { % 'q 9 ;{ J K{ W Wy e ez v uz  z  u  z  y  q    q  q  x  x  y , ,p : :p M :p M Mx ` bx s tp } }p  x  w  x      x                       / 0 C D V W c d t t                         % % - - = > R S ^ _ p p              x                       - - G H X Z l n } }                   * , < ? N O \ \ l l v v            x                       1 1 B B K K \ ^ g h y! z                     * * 3 3 F G Q R n n y y          w4 G / G 4 H 4 G * G 3 O + G / G 4 G 4 H 3 G 3 ,G ,4 >H @/ LG L/ TG T4 pG s4 G 3 F 3 F 4 G 3 F A F A F y"  (x* N G 'yY ~ v &x  $x  'x   $x 9 0 $y@ f ^ $xp  'x  )x  %x !  &w* O G wO .$.&This brought the spoilage in line, but'''Z v Y u Y u b v Y v Y v c v b $u $b 7u 8c J} IY ]u ]] ju j] qu q^ }u |Y u a t a t a t a { ` t X t X t ` s a { a #t #W )t )W 3s 3a Et EX Lt LX Wt XW at a` ut va s o z W t W t a t \ t \ t '&&&&W } t &W } *+==P^rq -:9FGPRabsu58GSefxy!#/1@AMNZ\dfwy* , ; <N Ob d t t   ( '       ) + < >D T^ `l w         4M2N;N;N:M:N;N;N</O02>NG;WNc;pNq;O<N2N1N2O;N2N< N ;N:*V42FNH;XNX;gNi2qNr1N;M2N6M:N~h|i|d{h|j}i}e}j|d!|!a4}5jD}KeV|Wkh}g`{}|`}j}j}j}a}j}i}a}j}j"|#i/}1j<}DjU}V`d}haz}|j|`}a}i|i~  *:MN\]mn~   ,-99Q9QRbbn~  )*:A[Zkkyy**9>\\ggyz}      : ;L Kj k} ~        5F GY [m      }#77#7$7 7$7$?%7$7'='%585%F7F$d8e%v7u$88%7%8 77%8$7$!7#184?=C2J=W$c8d$u777$7#7,0~MeReReIfJfRmSgSfJ$f&S6fCSSfbKtftJfSgIfRfJfSfSfS fReR+e8NCeDRUebSnfpSeRmJfSeReSf~|wwxw  !y25|?GTVxhjxstx|x|yx  x-0x8:IK[]}hixyw}(2NP`amo{  (78JJ\^mot 8UW_ars  ,78JL\s|    &   #$--::Ma y{{  ' ' 57 GG[\ k~   |9M9L8L5L4L:M9L:*M*56M61IMI0TMT:fMh:{T:N1M:M:M5L1M: L!14M31=M>:PMR:cUeHkM1M9K9L:M|g{g{g{h{gzh{b{hzh%|&h7{8_A{B_L{Kh^\vblcx{w_{h|h{h{h{h{h{h{_){-c9{:_M{Nh^|e_w{xhz`{h{hzg|)(67HI\\iizz(':;EEY`po},->ARTdgw"#57FQbdvw|  !3@NM]^lx78VWfgt|44 3< 44/44!%5/!@4B!R5S"b4cu45!5!4!4!5!<4!4!)5, ;4<!N<X!c4e!v<x 44!4 4 4|OcObOcFcOjObFcOcOcP#c3FEbGPWcXPdcfFocpOjOcObPcObFcObOb Ob]b/GFbHFYc\PlbnJybObKbObFbEbz}}}t}~u~ ~02~ALuVW~hj~vw~~~~~~~  ~(*~;=~NP~abulm~|}}~}t{%%19JJ[\on{{ ()66II[Zij{| ""4=XWiivwz #-:;GF YY ghuu  #+89JJhiy{6I6I6I6J7I6IDI-J7)J*6<J<6PQe7vJ7J7J7J6J-J7J6 QDO,16I7-IIK7[Jp6I6I6I6I6Jzdwdxdx[x[x\x\xey\%y;`HxH]Zy[elxo`yx\y[xeyey\xe x [x*e:x<dNwO`[x\dlxndxex_wdw[w{&2==PR_`ru #%00CDRR]fxzz,->FQRefv}#%36;D\]prz (/:;LNZ[ghxx %57HIT[kmwv y2122122 1 2.20=1DQ2Pc2dt1|2:222192 2 2 +1,:1CV2Wi1i{19111yL`LhL`L`MaM`C`C _ N`M*`+M<`<DPaPDZaYMlhwNaD`M`L`M`C`M`C_CaM(`)LG`GDQ`RL^`_Ll`mL~_~C_G_C`L_y{qr{q{rv|"#r56rA@sOMwZj{{||r|w||v|  r-q>@{PQ{cd{tt{rq{{x11FERRbbppv'(5MXXkm|  )*9;MO^_ky                    % & 7" 8K M X a r r               &= >Q S b c t u         x4 F 4 H / G 4 G 4 G 4 G 4 H + H 5 H 5 *H 55 NH O5 `H `4 sH t, ~H ~+ H 4 H 0 G + H 4 G + H 4 G 4 N 5 %G &4 7G E4 VG W3 cG q3 G 3 G * G 4 G ; ? yc ~ c v d w Z v Y v c w c w ^ v c v c ,w -c @w A[ Jw LZ ^w jc vw wc w c v c w c v ] u c v b v Y v (] 3u 4Y Fv Gb Xu bb nu pb } b u ] u b u b u x               # $ 4 6 F H Y Z d d v                  ! : E E S T e f p o        x                   - . ? ? F P a b u u                 ' ' 9 : D D U U b b p y          x               & & 7 9 G G W f r q                 % & 9 9 L N X X j l ~         x 0  0  1  1  1  1  0  1  &1 & 61 D V9 V d1 d v1 v 8  0  0  0  0  0  /  $0 $ 4/ 3 F6 F S/ ` q. r /  .  /  /  7 yK _ B _ L _ K ^ B _ L _ Z e K ` L &_ 'F 2_ 4B >` >C H` `G l_ lC ~_ L _ K ^ K ^ K ^ K ^ E ^ J $f %J 5] 6@ D^ >A O^ NJ ]] ^I j] I \ J ] J ^ J ] xq  z  z  y  z  q  u  z  { % 'q 9 ;{ J K{ W ez v uz  z  u  z  y  q    q  x  y , :p M :p M Mx ` bx s tp } x  w  x    x                   / 0 C D V W c d t t                   % - = > R S ^ _ p p            x                  - G H X Z l n }              * , < ? N O \ l v v        x                   1 1 B K \ ^ g h y! z                 * 3 F G Q R n y        w4 G / G 4 H 4 G * G 3 O + G / G 4 G 4 H 3 ,G ,4 >H @/ LG T4 pG s4 G 3 F 3 F 4 G 3 F A F Z v Y u Y u b v Y v c v b $u $b 7u 8c J} IY ]u ]] ju q^ }u |Y u a t a t a { ` t X t X t ` s a { a #t )W 3s 3a Et LX Wt XW at a` ut va s o z W t a t \ t <.?ʋS٬XX English EnglishTimes New RomanArial]4Customers wilI eat( anything a bakery( sells if it has5,",#,#5$:Q=/ZR\.xR{'Q/R/Q/R/R/5R5/ERE0rQu&R&Q&R0S0S'R'R47TVst##44SUpr5 7S Ua er t       F` 54444$SR`  $ ]enough chocolate,#E4i8FThWFsiwFiFv<i<jEj<vj<v<$:Q=/ZR\.xR{'Q/R/Q/R/R/5RE0rQu&R&Q&Q0S0S'R47TVst#4SUpr5 7S Ua er t      " %C F` E4i8FThWFsiwFiFv<iFi=iF!h%FCiGFbidFi<hFi>iEjQ?S =q English EnglishTimes New RomanArial nin it.,#$(EEVVbex||^./at a serious cost to the owner. He was( losing a lot of sleep. So he prevailed( upon the programmer to make the sys( tem ever smarter about error recovery.( (The owner couldn't quite admit that( those overpaid cretins he had so gladly( laid off earlier actually did bring a lot of( common sense to the party.)0NL%(-0 ')66CC SS aa mo          .. @@NNZYmn }}       ,, 88 QS de qe q0 L 93M49@L@0KLJ9]L^9qTq8L8L0L0L9L4L4L8L/K/L9L/'L'89L99KLJ8\S^FcLc/wLw/L8L0L0L9L9L9T9L9L9(L(9:L:0ELD0NLO9`L_0sL_0sLg+z+h>>gPzPgbzbbmzmbyzy^zhzgzggzg{ggyhzg/z.gOzOg_z_gmzmbvzvbzfzfzgzgz_{gzczc z ^{g/z/g8z8gE{FgYYgezfnrsfnrs""33RR]]mk}~!!--?ATTffyy*(:;LKZYmkqkq#$>?RSccrr35GIPS]]ll~ $$44?@SUegsgs""57HIUWggrr  12>?IK\]jjuu$ &//@BTV``r `r 3 !243<3=P3PW3W h4iw3s33 4 3 334 333 4 3#2#73: L3MV3W_2` q;qy3y3333344 3 ;  3  3%3%.3/ @3AM3MT3Tf2gt3gt3N&a'O8b9NVbXNubvNaNbNbNbNaNbNbNaJaJaNbI"a"I.a/FCbENUaUN]a]NoipNaNaJaNj]bCgCg0////q'/sTL'^rz%q's%r (t;3-Cjatj]/.Y"Prevailed" is a euphemism. The( owner yelled louder and more often and( paid his bills ever more slowly. The pro( grammer started losing sleep and miss( ing meals. In desperation, he began a( little systems analysis of his own. Even( tually, he found an old baker who was( willing to exchange a bit of practical( wisdom for the price of a few beers.Z '*'&*&'%ZDvTVtkl}y{}}}ts}sus  s|""|;;}MM}dd}ss|}t}}s|}t33tNMs`b}qb}q''ABTUfett{{   !33BBJJ[[no  //77IJ]]q]q():;EEXX``tt%%FFXWefvv~~**11DESSfeqeq)"(67HIfg##..ABNO[Zlm~"~#  >=IIVXdfpfp,!I!62I36EPE6RIR6qIs6H5I,H5ICH-I-I5I,I,I6H5%H&6;Q=6LHM5ZH[6lIm1xHz,H5H6IDO,I,I6I,I,J6I5*Q+6<I=5PIP5_I_6pI_6pI[w [)x+`6w7_BwD[MwNd]w]dfwfdrwsddw_wdwdxdwcwcxd x dwZ)w*d<=dJwKZTwVcbxbckwkd{w|ZwZw[w[wdwdwdxdwdxr x [w[.w.d?w@dQwQddwekppekpp!!46FHQR[\nlss  (*==KK\]efxx))55NQacoco./77BDNNWWjl)*=?OO__oo ++78ACSTefpfp./98DFZZkl ---=?OOWWhiww}}  &).).ZYYYY Dsq q'q*p#',pQI&Zpw*o&p'. $sq ]0.One by one, the programmer learned( the tricks for detecting baking disasters( in the making, and heading them off.( With each new bit of lore, the software( found fewer occasions to call the boss in( the middle of the night. (Today, we( would talk knowingly of expert systems,( fuzzy logic, and neural nets. But this( guy was just trying to refine a Fortran( program until it met specifications.) #*%(*$('(&C^1`r1s01181110,7100,1,111E8FT0Tf1fx9w111101110(1)618K1L\0\p1\p1F!` B4_5KE_EGL_LGY_XBq_XBq_qK^C_K_B_B_L`L_B_B_L_F^K ^ K1_2F?^@BJ_IK]__LpgpBw_wB_L_C_B_L`LgB_B_B_K_K(^(L5_6GC_CKT^SLa_bKo_bKo_qz11u??uLKq_`zppz~~zzqqzzz  z{12qGGqVVqhi{zzzqqz{uuq{z//z==zOOp^Xqihnhn:;DEPQddoo$%22<<NN]]ddmn~  ##=?OQ^_o_o" 12EFXZlluu#%/0CCVXccllww-.:<HHQQZZnZn  2 4 D D X X v v              ( * ; ; P P b cl m ~               + * 0 0 E E _ _ n _ n 3 ,F -2 >F >2 QF R* [G \) nF n) wF w- F 3 F ) F * F * F * E 3 F 3 G 2 F ) F 3 )G +3 =N ?* HF I2 [N [2 aG a3 rG r* F * F 4 G 3 G 3 O 4 G 4 G - F - F 3 G 3 N 3 F - 'F (4 8G 93 WF X3 dG gA mL gA mL X "u a 2u 4a Du Ea Uu Ua g} gW wu wW u a u a | X u a u p { a u a u b u X t X "u "b 6u 7b Hu Ha \u ]b ju kb {u |X v X u b u b u ] v b v p v Y v Y v a u \ &u &\ 6u 6] Au BX Uu TY `u _b mu _b mu  % % 8 : L L W W p q                         , . A A N N [ Z j j v v                       , . : : G H Z [ n [ n  % % 3 4 F E X W g f y y                       . / A A M M V V b c u v                       " % * , 9 , 9  Cp91#Bog_*pn%o(n*n  $) mO F (W m} u ' n ( 9 %p ^..UWhat finally pushed the software( over the line into "good enough" terri( tory came from a passing remark made( by the old baker. He observed over beers( one evening that customers would eat( just about anything a bakery sold if it( had enough chocolate in it. Thus was( born the ultimate error recovery strata( gem for the bakery control program V !( )M%)"V@ g g { {                     " " 7 7 L M [ Z m n ~ ~                   # " = = O O ^ ^ o ^ o  $/ " 4. 5 E. E S/ S ^/ ^ k. j .  .  /  .  .  /  .  /  /  /  .  /  )/ ) 8 : M7 O a/ ` q/ p .  /  /  /  0  /  7  0    /  */ * ;/ : I/ H a0 H a0 b# l( b# l( E \ J 0] 1I =\ >I Qd QI Y^ YI i] jI {] |J ^ I ] @ ^ @ ] J ] I ] J ^ J ^ J ] J !^ !J 5e 7J I] JK X^ YJ d^ fA n^ nJ ^ K f J ^ J ^ J ^ J ^ J ^ K ^ B ^ B ^ K 5_ 7J H^ IA [^ ]K m^ ]K m^ p $ &x 8 8t = =t J Jp ] _y n ny u uy  p  o  o  o  x  o  z  y    p  p . 0y A Ay G Gz Y Zp k my y {z  z  y  y  p  p  y  y  z  y  p  p . 1z A Ay Q Qz _ `y l `y l  " $ 5 8 G G V V e e u v                     ' ' 8 8 N O [ \ g h x y                   . . > > N N ` a m a m    / 1 < > J J W W g i { }                     1 4 G G U U e e r r                     & & 4 4 < < L L W W ` ` l ` l  % % 6 8 K K Y Y i j { ~                   2 3 = > P R ] ^ l l { {                     " " 2 2 K M ] _ k _ k + $G %3 6G 64 CF F4 WG W. `F `. mF l* G 4 F 3 F 3 G + G / G * G 3 G 3 G . F 4 G 3 %F %4 6F 63 EF F4 TG U3 fG f3 sF s3 zF z4 G 4 F 3 F 3 G 3 E 3 E 3 F 2 N 2 F 2 E - !F 3 .F /3 AF B. NE M3 `F `: k? `: k? b #~ $b 4u 4a Rv RX ^u ^X lu ja |v |b v ] u ] t Y v c u Y u Y u b u Y u b v b )u )a =} =a Iu Ib Yt Ya jt ja |t }] t a t a t X u X u a | a t a t ` { ` s ` %t &` Dt Ch ml Ch ml VUUUU @ o ! l7 / (@ mf ^ %o l ) m % l ( k  %* kN F )X m~ u # o~ r$(EVbex| ')6C Sa mo        .. @NZYmn }      ,8 QS de q0 L 93M49@L@0KLJ9]L^9qT8L0L9L4L8L/K9L/'L'89L99KLJ8\S^FcLw/L8L0L9L9T9L9L9(L(9:L:0ELD0NLO9`L_0sLg+z+h>>gPzPgbzmbyzy^zhzggzg{ggyhzg/z.gOzOg_z_gmzvbzfzgzgz_{gzc z ^{g/z8gE{FgYYgezfnrs""33R]mk}~!-?ATTffyy*(:;LKZYmkq#$>?RScr35GIPS]l~ $4?@SUegs""57HIUWgr  12>?IK\]ju$ &//@BTV``r 3 !243<3=P3W h4iw3s3 4 3 334 33 4 3#2#73: L3MV3W_2` q;y333344 3 ;  3%.3/ @3AM3Tf2gt3N&a'O8b9NVbXNubvNaNbNbNaNbNbNaJaNb"I.a/FCbENUa]NoipNaNaJaNj]bCgDvTVtkl}y{}}}ts}su s|";}Md}ss|}t}}s|}3tNMs`b}q''ABTUfet{   !33BJ[[no  /7IJ]]q():;EEX`tt%FFXWefv~*1DESSfeq)"(67HIfg#..ABNO[Zlm~"# >=IIVXdfp,!I!62I36EPR6qIs6H5I,H5ICH-I5I,I6H5%H&6;Q=6LHM5ZH[6lIm1xHz,H5H6IDO,I6I,J6I5*Q+6<I=5PI_6pI[w [)x+`6w7_BwD[MwNd]wfdrwsddw_wdwdxdwcxd x dwZ)w*d<=dJwKZTwVcbxkd{w|Zw[w[wdwdxdwdxr x[.w.d?w@dQwQddwekpp!!46FHQR[\nls (*=K\]efx)5NQaco./77BDNNWWjl)*=?O_o ++78ACSTefp./98DFZZkl ---=?OWhiw}  &).C^1`r1s018110,700,11E8FT0Tf1fx9w11110110(1)618K1L\0\p1F!` B4_5KE_LGY_XBq_XBq_qK^C_K_B_L`L_B_L_F^K ^ K1_2F?^@BJ_IK]__LpgwB_L_C_B_L`LgB_B_K_K(^(L5_6GC_CKT^SLa_bKo_qz1?uLKq_`zp~zzqqzz z{12qGVqhi{zzzqqz{uq{z/=zOOp^Xqihn:;DEPQdo$%2<NN]dmn~  ##=?OQ^_o" 12EFXZlu#%/0CCVXclww-.:<HQZZn  2 4 D X v v           ( * ; P b cl m ~              + * 0 E _ _ n 3 ,F -2 >F >2 QF R* [G \) nF w- F 3 F ) F * F * E 3 F 3 G 2 F ) F 3 )G +3 =N ?* HF I2 [N a3 rG r* F 4 G 3 G 3 O 4 G 4 G - F 3 G 3 N 3 F - 'F (4 8G 93 WF X3 dG gA mL X "u a 2u 4a Du Ea Uu Ua g} wW u a u a | X u a u p { a u b u X t "b 6u 7b Hu Ha \u ]b ju kb {u |X v b u b u ] v b v p v Y v a u \ &u 6] Au BX Uu TY `u _b mu  % % 8 : L W p q                     , . A N [ Z j v                   , . : : G H Z [ n  % % 3 4 F E X W g f y y                 . / A A M V b c u v                       " % * , 9 @ g g { {                  " 7 7 L M [ Z m n ~ ~               # " = = O O ^ ^ o  $/ " 4. 5 E. E S/ ^ k. j .  .  .  .  /  .  /  /  .  / ) 8 : M7 O a/ ` q/ p .  /  /  0  /  7  0    */ * ;/ : I/ H a0 H a0 b# l( E \ J 0] 1I =\ >I Qd YI i] jI {] |J ^ I ] @ ] J ] I ] J ^ J ] !J 5e 7J I] JK X^ YJ d^ fA n^ nJ ^ K f J ^ J ^ J ^ J ^ K ^ B ^ K 5_ 7J H^ IA [^ ]K m^ p $ &x 8 =t J Jp ] _y n uy  p  o  o  x  o  z  y    p . 0y A Gz Y Zp k my y {z  z  y  y  p  y  y  z  y  p . 1z A Ay Q Qz _ `y l  " $ 5 8 G V e e u v                  ' 8 8 N O [ \ g h x y                 . > N N ` a m    / 1 < > J W g i { }                   1 4 G U e r                   & 4 < < L W ` ` l  % % 6 8 K Y i j { ~                 2 3 = > P R ] ^ l {                 " 2 K M ] _ k + $G %3 6G 64 CF F4 WG `. mF l* G 4 F 3 G + G / G * G 3 G 3 G . F 4 G %4 6F 63 EF F4 TG U3 fG f3 sF z4 G 4 F 3 F 3 G 3 E 3 E 3 F 2 N 2 E - !F 3 .F /3 AF B. NE M3 `F `: k? b #~ $b 4u 4a Rv ^X lu ja |v |b v ] t Y v c u Y u b u Y u b v b )u )a =} Ib Yt Ya jt ja |t }] t a t a t X u a | a t a t ` { ` s ` %t &` Dt Ch ml /vٟP English EnglishTimes New RomanArial :.subroutine CHOCOLATE.%&24<>QSbbkkx{U..Whenever the program determined( that a batch of dough would be edible( but unappetizing, it dumped in enough( chocolate to cover up the shortcomings.( The further out of specification the( dough, the more stuff added by subrou( tine CHOCOLATE. And it sold.F&(%'$&67IL\[jl||%&79UUbbtv    &&89 LMYZ ij||    ' 77 HI [\efxx       1M9L5M5M: M:M!:2M4:FTG:ZU\:kMl5xLy1M:M0M9M:UHS0M0M5M1M1M:L;9M<:MUO;^M_0oMo0{M{0L:M:M:L:M:M:L;U1 M1 Mh|_|i|h|h|`|i0|2c>{>hO|OcW|Wcd|cht|th|||h|h|h{i|i|h|h{ic|c|_#}$i3|3h<|<hH|J_]|]hm|nh{|}c|h|h|h|_|h|ih | w { w {//=>ML`aqq~~  //@@OOYZlZll}}     ##--99NO``hh  00CDUTffoo      ,.<=LM\_ljxz!!++>@F@F   '&0 UM&_ |( % 'F U..>Lest you think this yet another sign( of computer-inspired moral decay, real( ize that bakers have been pulling tricks( such as this one for centuries. (When I( was a kid, it was commonplace for( mothers to foist off aging milk as a yum( my chocolate drink.) Expert systems( must get their expertise where they can( find it.? %()("*$( ?6"5# 6!-5-868"L=K#]6]"o5o}6}665"666566" 6 "6#+>+#;5;G5GS6S#c6e"u5w"655#6#6"6"55#>" 5" 5QeGdGdQdQeQ e!Q4l5PJdKMWdXQgdhQudvX]HdQdPdQlHdQdQdHdHdQ e!Q2e3Q@dBQQdTH]d]HdddHucwQeQdQdPl_jQdQdPcQdH d X \ X \v{{w "{..v88vKM^^wqrvvww )+<<GGXYkmwuwvw{{vvw       **66ACVX`bmmyy !"-.ACYCY[ijvy       22FEQQdekk  :<YZjk~           )* 66??LL ]]ddsp     &  .&. 66 SU]\hg{{      &       8L8T8L8 K 0 L!94L38ELF9XLX0aLa8sLt4L9L0L0L9L/L9L0LGL.R.L06L78HLH9[T\9lLk8yK{4L4L8L8S9L4K8K9 L 8 K 8 Kgzgzgzbybzg!!g2z2b@z@bHzHbUzU^hzigyzx^zgzgzgzgzggyh{cz^zgzh"{"g)z)gCyD_W{Whhzgguzuhzbzbz^zhzgfzfzgzg zg z?>>>>  >6%G ld(v ) ( " &*. TL$^ z( X/.My reason in telling this little tale is( to focus on the business of error recov( ery in embedded systems. I've been dis( cussing other aspects of this topic in re( cent essays. In "Staying Alive" (Dec.( 1993, pp. 89-92), I observed that an em( bedded system must keep going at all( costs. You simply can't afford to have a( controller hang or go nutty, regardless( of the provocation. Last month ("Who( Cares?" Feb. 1993, pp. 89-92), I fault( ed a set-up program I used for clobber( ing a PC ROM BIOS and paralyzing a( computer for several weeks. You have to( make sure that even the support tools( for an embedded system are sufficiently( robust.RS&%)Z (#(&(  ((68HJZ\hiz{  ''23EFOQ]]ggnqz|     $&22??PRccpp{|  ''33DERR\\kkyz      2 3;33 3 3 (3) H3I\3^ m2m33 233 3: 33 3  '3( 438.=3=H3HT4V\!^ m2o 333 2 3 3333  3 ' + ' +NaNaNaNaEaNbN)i)N3b3NEbFJRaSEeagNvbwNaNbNaNaNiNaMaJaNbMbMbE#a#E+b+J6a7EJbKFTaUN`a`IkbkIw`wNbNiEaNbDbDaNaNbOaN a U Y U Y|}}ww  }|%'|35}GI|[\|hkqqtt|vvsx}|t}%'|99tHHtdcsmoszx|}uqqs}|       ((=?DDNN]`qs} ((9:JH]]ddoo     ''66DEXXeerr+*;:MM[[ml       1/BBWW__lmyx""  !!23B<LJ\[ii}}  5H6I5I0H6I 5I,$I%,/H06AIB6PHP+\H\+oIp6I5H5Q5H5H5I5I5P5H5H5!I"55H60BIC1OHN5aP^CeNe5tIt6I5H5P5I5H+H,I5H5H 5 H 5 Hcw[x[w_w[wdwcwc/0d?w@dQxQcavbcsxsdwcw^w[wdwcwrx[w[wcwdw_*w*_5w5dRwScdwecwwy^w[wYwY}\gZv[wc vc v"&55CCYZjj}))7;KNX[jm       *+78LN``jj{|   !-/?@RR\\jhyz        !">>HHdd "35IIQQb duv    010 8 0 ,0-?1>M1MT1Tb0`q1q0101000111 0 1-1-A1@M1P,U1U^1^{1w10110/010 0 0K_K^B^L _ K^K&^'K<_=KL_MK]^]Gj^jGv^vB^K^F^F^K^K]L^K^G^G_C&_'K7^7KE^EKR_RKf^fLygzLgK_L_F^F^F^K_K_B^J ^J ^pzzzzzzz))zJJq]^zonqpzppyzztz  z))z11zBC{PQzaaziizvvzpppzpzzvqz z      ) ) ;3(D ib+q & ) % ")+ QH(Y w% ( ( # 81(B g^&p (  Y/.I can't provide a simple recipe for( making robust systems, although I have( often been guilty of promulgating var( ious guidelines. Instead, I have learned( to be on the lookout for anecdotal cases( that illustrate useful techniques for( keeping systems alive. One of my favor( ites is subroutine CHOCOLATE. And here( are a few more that might inspire you in( designing some future product. $'P)&(")$&9<CERR``st88LLTVffvv           + + 3 3 A B T Tg h { |                     " " 2 4= > K K] _ p p                 2 G * G . G 3 G 3 G * G * "G $3 5G 74 GF G3 ZF Z3 gG g3 yN y3 F ) F * G . F 3 O 3 G 3 G * G * G 3 N 4 G 3 &G '3 EF F3 YF Y) bF d3 vO w3 F . F ) G 4 G 3 N 3 G 3 F 3 G 3 G  : ?  : ? X u a v b u a u a u b } b "u $X /u /Y Cu Db Tu VX _u `Y iv hb |u }b u a v p u Y u Y u a u b u ] u a u b u X u p '{ 'Y 2v 2Y @v @Y Ju JY ]u ^a nu ob u b u Y u Y v b u b u b u b u b u Y u Y u                / / 8 8 F E Y Z j j r r } |                     " " 2 4 F H W X h i { |                                 ! ! - , A B O P ] \ j j | |                   % % 1 2 B B R R f g y z                               / / 7 7 D D X X e e r r                       ) * = > O O U U h g u u z z                   /  /  /  /  /  0  0  !0 ! /0 / D0 D X/ Y g0 g y/ x /  /  /  /  /  /  /  /  /  /  "/ # 20 4 A0 @ N/ O ]/ _* g0 g v/ v /  0  /  /  /  .  /  /  / J ^ K ^ K ^ J ^ K ^ A ^ A ^ J #^ $J ?] ?J G^ GJ e^ gJ w^ xJ ^ J ^ E ^ E ] A ^ J ^ E ^ E ^ J ^ A ^ J e A 0^ 2F =^ =A E^ EA N^ NJ `^ cK n^ oJ f A ^ K ^ K ^ J ^ J f I ^ J ] @ ^ @ ] J ^ J ^ p  y  y  o  z  y  p ! "y 6 8y J Jy T Ty ` ay r sy  y  o  o  y  u  y  y  z  y  y " #y / 0y B Bp T Vy i jy y zt        $  ') O G 'X } u ) ) &  ( 0 / '@ f ^ )o   . FAKING IT              . . : : B C [ C [     [  [ W.wYou might characterize the lesson to be( gleaned from the bakery story as, "Give( the customers something they're willingx(Px           & & 9! : N N Z Z c c r s                       ( ( 3 4 G H W W a a j k z {                      4 O * G 4 F 3 G 4 G 4 F + -G -* 4G 4* DG B3 QF Q4 bG b3 F / F / G * G 3 F + F + G 3 G * G 4 G 4 G 3 (N (3 /G /3 <G =. IF I2 [F [3 iF i3 |N |3 F 3 F 3 G A L , F , 6 * G ) F 3 E 4 F 4 F ] u Y u a t a t a u b t a u ] *u *a =u =a \u ]b mu mb {u {a t a t a u a u a u b t ] t X u X u a t a -| -] 1t 1] >t >X Rt Ra dt ca u| vW }b ~a t b t a t a s X s X t X t X s a s a | a | xwwww !  () O F (W | t ' | %&24<>QSbkx{$&67IL\[jl||%&79Ubtv   &89 LMYZ ij|    ' 77 HI [\efx    1M9L5M: M:M!:2M4:FTG:ZU\:kMl5xLy1M:M0M9M:UHS0M5M1M:L;9M<:MUO;^M_0oM{0L:M:L:M:M:L;U1 Mh|_|i|h|h|`|i0|2c>{>hO|Wcd|cht||h|h|h{i|i|h{ic|_#}$i3|<hH|J_]|]hm|nh{|}c|h|h|h|_|h|ih | w {//=>ML`aqq~ //@@OOYZlZll}}   #-99NO`h 00CDUTfo    ,.<=LM\_ljxz!!++>@F6"5# 6!-58"L=K#]6]"o5}665"66566" 6#+>+#;5;G5S#c6e"u5w"655#6#6"55#>" 5QeGdQdQeQ e!Q4l5PJdKMWdXQgdhQudvX]HdQdPdQlHdQdQdHdQ e!Q2e3Q@dBQQdTH]ddHucwQeQdQdPl_jQdPcQdH d X \v{w "{.8vKM^^wqrvw )+<GXYkmwuwvw{vvw    *6ACVX`bmy !"-.ACYCY[ijvy   2FEQQdek  :<YZjk~         )* 6?LL ]dsp     &  .&6 SU]\hg{    &     8L8T8 K 0 L!94L38ELF9XLX0aLa8sLt4L9L0L9L/L9L0LGL.R06L78HLH9[T\9lLk8yK{4L8L8S9L4K8K9 L 8 Kgzgzgzbyg!!g2z2b@zHbUzU^hzigyzx^zgzgzgzggyh{cz^zgzh"{)gCyD_W{Whhzgguzuhzbz^zhzgfzgzg z  (68HJZ\hiz{  '23EFOQ]gnqz|   $&2?PRcp{|  '3DER\kkyz    2 3;3 3 (3) H3I\3^ m2m33 23 3: 33 3  '3( 438.=3HT4V\!^ m2o 33 2 3 333  3 ' +NaNaNaNaEaNbN)i3NEbFJRaSEeagNvbwNaNaNaNiNaMaJaNbMbE#a+J6a7EJbKFTaUN`akIw`wNbNiEaNbDaNaOaN a U Y|}}w }|%'|35}GI|[\|hkqt|vsx}|t}%'|9Htdcsmoszx|}uqs}|    ((=?DN]`qs} ((9:JH]doo   '6DEXXeerr+*;:M[ml    1/BBW_lmyx""  !23B<LJ\[ii} 5H6I5I0H6I 5I,$I%,/H06AIB6PH\+oIp6I5H5Q5H5I5P5H5!I"55H60BIC1OHN5aP^CeNt6I5H5P5I5H+H,I5H5H 5 Hcw[x_w[wdwc/0d?w@dQxQcavbcsxsdwcw^w[wdwcwrx[wcwdw_*w5dRwScdwecwwy^w[wY}\gZv[wc v"&5CYZjj})7;KNX[jm     *+78LN`j{|  !-/?@R\jhyz     !">Hdd "35IQb duv   010 8 0 ,0-?1>M1Tb0`q1q00100011 0 1-1-A1@M1P,U1^{1w1010/00 0K_K^B^L _K&^'K<_=KL_MK]^jGv^vB^K^F^K^K]L^K^G_C&_'K7^EKR_RKf^fLygzLgK_L_F^F^K_K_B^J ^pzzzzz))zJJq]^zonqpzpyzztz  z)1zBC{PQzaizvvzpppzpzzvqz    $&9<CER`st88LLTVfv          + 3 A B T Tg h { |                   " 2 4= > K K] _ p p             2 G * G . G 3 G 3 G * "G $3 5G 74 GF G3 ZF g3 yN y3 F ) F * G . F 3 O 3 G * G 3 N 4 G 3 &G '3 EF F3 YF Y) bF d3 vO w3 F . F ) G 4 G 3 N 3 F 3 G 3 G  : ? X u a v b u a u b } b "u $X /u /Y Cu Db Tu VX _u `Y iv hb |u }b u a v p u Y u a u b u ] u a u b u X u p '{ 2Y @v JY ]u ^a nu ob u b u Y v b u b u b u b u b u Y u            / 8 F E Y Z j r } |                  " 2 4 F H W X h i { |                            ! ! - , A B O P ] \ j j | |                % 1 2 B B R R f g y z                            / 7 D D X X e e r r                   ) * = > O U h g u z                /  /  /  /  0  0 ! /0 / D0 D X/ Y g0 g y/ x /  /  /  /  /  /  /  /  /  "/ # 20 4 A0 @ N/ O ]/ _* g0 v /  0  /  /  .  /  / J ^ K ^ K ^ K ^ A ^ J #^ $J ?] GJ e^ gJ w^ xJ ^ J ^ E ] A ^ J ^ E ^ J ^ A ^ J e A 0^ 2F =^ EA N^ NJ `^ cK n^ oJ f A ^ K ^ K ^ J f I ^ J ] @ ] J ^ p  y  y  o  z  y  p ! "y 6 8y J Ty ` ay r sy  y  o  y  u  y  y  z  y " #y / 0y B Bp T Vy i jy y zt               . : B C [          & & 9! : N N Z c r s                      ( 3 4 G H W a j k z {                4 O * G 4 F 3 G 4 G 4 F + -G 4* DG B3 QF Q4 bG b3 F / G * G 3 F + G 3 G * G 4 G 4 G 3 (N /3 <G =. IF I2 [F [3 iF i3 |N 3 F 3 G A L , 6 * G ) F 3 E 4 F ] u Y u a t a u b t a u ] *u *a =u =a \u ]b mu mb {u {a t a u a u a u b t ] t X u X u a t a -| 1] >t >X Rt Ra dt ca u| vW }b ~a t b t a s X s X t X t X s a s a | jNx[•  English EnglishTimes New RomanArial?*MARCH 1994 EMBEDDED SYSTEMS PROGRAMMING 81++     $ $ < < X X c c m r                   4 5 F G [ [ c c w w                   3 4 G H \ [ q r                +**** * %     $ $ < < X c m r                 4 5 F G [ c w w                 3 4 G H \ [ q r             @6&.DfLP^ $  ^" >$t&"(d "& .$r $  n  ~ " uFR5S